A motor vehicle includes a prime mover, a transmission, as well as a driven end, wherein the transmission is connected between the prime mover and the driven end. The transmission converts rotational speeds and torques and, in this way, makes the available tractive force of the prime mover available at the driven end. Motor vehicles also include a starting component.
The starting component can be a torque converter including a torque converter lockup clutch or also a master clutch, wherein the master clutch can be a transmission-internal or transmission-external master clutch. The prime mover of the motor vehicle can be an internal combustion engine or an electric machine/motor or also a hybrid drive which includes an internal combustion engine as well as an electric machine/motor.
When the prime mover is a hybrid drive, a separating clutch is typically connected between the internal combustion engine and the electric machine in order to turn off or bring the internal combustion engine to a standstill when the separating clutch is disengaged and to subsequently utilize the electric machine for driving the motor vehicle.
When the torque converter lockup clutch is engaged in a motor vehicle including a torque converter or when the transmission-internal or transmission-external master clutch is engaged in a motor vehicle without a torque converter, and when, in addition, the transmission is friction-locking, i.e., when the prime-mover rotational speed is coupled to the driven-end rotational speed via the transmission ratio, it can become necessary due to an operational event to decouple the rotational speed of the prime mover from the driven-end rotational speed in order to change, in particular, increase the prime-mover rotational speed, decoupled from the driven-end rotational speed.
This can be necessary, for example, when, a motor vehicle including a hybrid drive which is operated purely electrically is situated on an uphill incline, as viewed in the direction of travel, and the power transmission capacity of the torque converter lockup clutch or the power transmission capacity of the launch clutch is too low in order to transmit a torque required for the starting operation in the direction of the driven end. Furthermore, it can also be necessary, for example, to increase the prime-mover rotational speed when a state of charge of an electric accumulator is too low and the electric accumulator is to be charged via the prime mover.
When the torque converter lockup clutch is engaged or the master clutch is engaged and the transmission is friction-locking, if the prime mover is to be decoupled from the driven end, the approach taken in methods for operating a motor vehicle known from practical experience is that the power transmission capacity of the torque converter lockup clutch or the power transmission capacity of the master clutch is reduced by an appropriate reduction of the pressure control thereof. As a result, the torque converter lockup clutch or the master clutch is subsequently brought into a slip operation in order to thereby decouple the prime-mover rotational speed from the driven-end rotational speed and to subsequently preferably increase the prime-mover rotational speed, decoupled from the driven-end rotational speed. Due to the reduction in the power transmission capacity of the torque converter lockup clutch or the master clutch by the corresponding reduction of the pressure control, less torque can be transmitted in the direction of the driven end, and therefore the process of bringing the torque converter lockup clutch or the master clutch into a slip operation is noticeable at the driven end. As a result, when the motor vehicle is located on a hillside, the motor vehicle can be caused to roll backward on the hillside.
DE 10 2006 018 058 A1 describes a motor vehicle including a hybrid drive, a starting component designed as a torque converter, and a transmission. Various starting processes for the motor vehicle are disclosed in this prior art, in which the power transmission capacity of the torque converter lockup clutch is changed in order to transmit a drive torque, without slip, from the torque converter lockup clutch in the direction of the driven end.
DE 10 2015 208 402 A1 describes yet another motor vehicle including a hybrid drive, a starting component designed as a torque converter, and a transmission. In this case, when a decoupling is requested, the torque converter lockup clutch is brought into a state of slip and, when the slip at the torque converter lockup clutch is equal to or greater than a limiting value, a target rotational speed for the electric machine of the prime mover is subsequently specified.